The invention is based on a main brake cylinder as generally defined hereinafter. A brake cylinder of this kind is known from German Offenlegungsschrift No. 27 23 734.
In the known main brake cylinder, the two brake circuits are connected in series both geometrically and in terms of their function, in the manner of a hydraulic dual-circuit tandem main brake cylinder. A control valve establishes the communication of the pressure source with a brake piston disposed in the amplifier cylinder, and the pressure in the other brake circuit is established by means of the displacement of a further piston under the influence of an auxiliary force. The control valve is disposed in the interior of the first piston, which in turn is supported in the amplifier cylinder.
In such brake systems, to be able to perform an arbitrary feeding of pressure, for instance in order to monitor the brake system as a whole, to regulate drive slippage or to effect an automatic interval or stopped braking, magnetic valves must be separately disposed in the brake lines, by way of which valves then when they are actuated accordingly the desired pressure can be fed into the brake circuits from a pressure source. Such provisions are complicated and expensive, because if pressure is to be fed into two brake circuits, for example, one magnetic valve or possibly a multiple-position valve as well has to be provided for each brake circuit.